The use of speech systems is commonplace. For example, in teleconferencing systems, participates typically gather in an office or meeting room and are seated at various locations about the room. The room used is typically not equipped with special sound tailoring materials, and echoes of both near and far-end voices add to the noise level. If the room is large enough, some participates may be seated away from the conference table, distancing themselves from the microphones. Some participates may not actively speak, or may contribute only occasionally. Their presence, however, adds to the number of sources of room noise as pencil tapping, paper rustling, and side conversations develop. These noise sources further degrade the sound quality experienced by the far-end parties.
The majority of speech systems have microphones deployed at one, two, or at most three locations. The microphones are typically positioned on the surface of a conference table, distributed in a manner that provides the best pickup of the most significant contributors to the meeting. This selection of microphone positions may make some of the contributors difficult to hear. Occasional participants are frequently forced to move closer to a microphone when they speak, creating additional room noise as they switch seats or move chairs.
Microphone arrays are generally designed as free-field devices and in some instances are embedded within a structure. A problem with prior art microphone arrays is that the beam width decreases with increasing frequency and sidelobes become more problematic. This results in significant off axis “coloration” of the signals. As it is impossible to predict when a talker will speak, there is necessarily a period time during which the talker will be off axis with consequential “coloration” degraded performance.
Microphones with “pancake directivity” for use in speech systems are known. For example, arrangements of directional microphones covering 360 degrees in the horizontal plane exist in the telecom and conference speaker phone art. In order to make conference speakerphones effective people have used various arrays of microphones. Systems that provide directivity in microphone are expensive and complex and they do not provide a consistent beam shape over the frequency range of use. Directional microphones are known for use in speech systems to minimize the effects of ambient noise and reverberation. It is also known to use multiple microphones when there is more than one talker, where the microphones are either placed near to the source or more centrally as an array. Moreover, systems are also known for selecting which microphone or combination to use in high noise or reverberant environments. For example, in teleconferencing applications, it is known to use arrays of directional microphones associated with an automatic mixer. The limitation of these systems is that they are either characterized by a fairly modest directionality or they are of costly construction.
Another issue is the speakerphone type systems can manifest different types of echoes. For example, acoustic echo from feedback in the acoustic path between the speaker of the phone and its microphone. Another example is line echo that originates in the switched network that routes a call between stations. Acoustic feedback is a problem in speakerphones and known systems often incorporate some type of expensive electronic circuitry adapted to suppress, cancel, or filter out unwanted acoustic echo during use.
It would useful to have a microphone array that is less expensive, less complex and provides more consistent performance over the appropriate range of verbal frequencies in certain environments such as, but not limited to, teleconferencing. Accordingly, there is a long-felt but as yet unsatisfied need in the field for a speakerphone design that inherently reduces the amount of acoustic echo present in the phone, thereby resulting in the need for less complex, and hence, less costly echo cancellation circuitry, and one that also provides better low-frequency sound definition and high-frequency sound dispersion by the loudspeaker of the phone. There is also a need for devices, methods and systems for microphone arrays that allow for greater flexibility in the placement in the microphone. There is also a need for devices, methods, and systems for speakerphones that have improved echo cancellation, better sound performance and dispersion, and require a substantially smaller footprint than speakerphones of the prior art.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present disclosure as set forth in the present application with reference to the drawings.